The calibration of radiocarbon ages to calendar ages requires comparing radiocarbon measurements against independent chronological records — primarily tree rings, which provide a year-by-year record of atmospheric radiocarbon going back more than 12,000 years, and for periods beyond that, records from corals, speleothems (cave formations), and other sources.

The calibration process converts radiocarbon years into calibrated calendar years — “cal BP” in the literature — and the result is typically expressed as a range of probable calendar ages rather than a single point estimate, reflecting the uncertainty in both the radiocarbon measurement and the calibration curve.

AMS — accelerator mass spectrometry — is the method used to measure the actual ratio of carbon-14 to carbon-12 atoms in a sample, rather than simply counting the decay events (which is the older conventional radiocarbon dating approach).

AMS requires only tiny samples — milligrams of material rather than grams — which is crucial for dating precious archaeological specimens like the Bluefish Caves bones, where consuming large amounts of material would destroy much of the evidence.